Process for the manufacture of double salts of niobium chloride and tantalum chloride



Dec. 11, 1962 W. SCHELLER ET AL PROCESS FOR THE MANUFACTURE OF DOUBLE SALTS OF NIOBIUM CHLORIDE AND TANTALUM CHLORIDE 'Filed March 8, 1960 lllllllllll INVENTORS M d? Md er m we n m W Wk w FIG 2 ATTORN EYS inc 3,068,066 PROCESS FoR THE MANtJrAc'rURn or noUnLE This invention provides a process for the manufacture of double salts of niobium chloride and tantalum chloride.

The processes used for the manufacture of the metals, niobium and tantalum, such, for example, as reduction with an alkali metal or alkaline earth metal or hydrogen or similar reducing agent, or the electrolytic method, generally use as starting material the pentachloride of the metal to be obtained. Having regard to the high temperatures at which these processes are generally carried out, the relatively low boiling points and high vapour pressures of the pentachlorides are disadvantageous as they lead to losses of material or necessitate special apparatus to avoid such losses. 'In order to avoid these disadvantages it has been proposed to use, instead of pentachlorides, double salts of the metals, more especially the known alkali metal halide double salts, for example,

KTaCl KNbC1 xeracu KFNbCl which have low vapour pressures above their melting points.

It has also been proposed to use, instead of the normal double salts, reduced or low valent double salts, that is to say double salts in which the tantalum or niobium has a valency less than 5. Such low valent double salts generally decompose under lower pressures than do the double salts of normal valency. A further advantage of the use of the lower valent double salts in obtaining the metals by electrolysis is that it is necessary in the cell only to bring about the residual reduction to form the metal, that is to say, to reduce the valency to zero. Accordingly, a part of the reduction process takes place outside the cell in a preliminary stage for making the reduced double salt, whereby the output of the cell is increased.

The present invention provides an especially advantageous and simple process for the manufacture of double salts of an alkali metal or alkaline earth metal halide with thechloride of niobium or tantalum. In the process of this invention the vapour of the chloride of niobium or tantalum, and especially the pentachloride, is reacted with a solid alkali metal or alkaline earth metal halide of course particle size at a temperature above the melting point of the double salt to be formed, and the liquid double salt is withdrawn from the reaction zone. The invention also provides an apparatus for carrying out the process.

When the process is used for making low valent double salts the vapour of the pentachloride is reacted with the solid halide in the presence of hydrogen.

The invention is more fully described below with reference to the accompanying drawings, which illustrate apparatus suitable for carrying out the process.

Advantageously the reaction is carried out by introducing the vapour of the pentachioride in an upward stream through a vertical reaction vessel containing the solid alkali metal halide of coarse particle size, by continuously or periodically withdrawing the double salt from a heated bottom vessel disposed below the reaction vessel, and supplying the solid alkali metal halide to the upper part of the reaction vessel as the halide is consumed.

Advantageously an inert atmosphere is maintained in the reaction vessel.

The process of this invention enables the pentachloride double salt to be made in a continuous manner with very simple apparatus, in a favourable yield and in the form of an extremely pure product, that is to say, a product containing substantially no free pentachloride. Having regard to the temperature of the liquid double salt that collects in the bottom vessel no pentachloride can remain in the residue contained in the bottom vessel. The pentachloride therefore enters the upwardly flowing stream of pentachloride vapour and is reacted in the reaction vessel.

The invention also enables double salts to be obtained which are very nearly free from oxygen. This is important, especially in view of the fact that oxygen-containing compounds are occasionally present in the starting material, such as the oxychlorides, which are formed as byproducts in the usual chlorination processes. Owing to their low sublimation temperature, these oxygen-containing impurities do not enter the bottom vessel, but escape from the upper part of the reaction vessel. The ability to produce oxygen-free double salts is a special advantage of the process of this invention, because production of a material having the required low oxygen content in the usual processes (electrolysis or metal reduction) requires the use of a starting material having a similarly low oxygen content.

For the uses hereinbefore mentioned there are suitable as double salts, especially the potassium chloride or potassium fluoride double salts. In these cases potassium chloride or fluoride of coarse particle size is introduced into the reaction vessel.

When the process is used for the production of a reduced double salt the temperature of the bed of coarse particles is above the temperature at which the reaction product to be obtained is liquid. The product that flows away from the reaction zone is the double salt or the eutectic mixture of the low valent double salt formed and the alkali metal or alkaline earth metal chloride present in the reaction zone. The temperature in the reaction zone is maintained at a value between the melting point of the double salt formed or of the eutectic mixture of reduced double salt and alkali metal or alkaline earth metal chloride, and the melting point of the chloride itself, and is not below 550 C. A temperature of 550 C. is also below the temperature at which reduction of the double saltto metal takes place and below the melting point of the chloride supplied.

By the process of this invention the reduced double salts of niobium or tantalum can be obtained in an extra ordinarily simple manner and in a pure state, that is to say, free from the pentachloride used as starting material. The reduced double salt so obtained is, for example, the tantalum potassium chloride double salt having the formula K TaCI in which the tantalum is tetravalent, or the niobium potassium chloride double salt having the formula K NbCl in which the niobium is trivalent. However, it will be understood that the process is not limited to the production of these double salts.

The examples given below illustrate the invention with reference to the accompanying drawings. These examples illustrate the production of single double salts, but it is to be understood that mixtures of a niobium double salt and a tantalum double salt can be made by starting from an appropriate mixture of the pentachlorides of those metals. This is especially advantageous when the double salts are to be used for making alloys of the two metals.

The apparatus shown in FIGURE 1 serves for the production of a pentavalent double salt and consists of a vertical reaction vessel it) having a length of 70 centimeters and a diameter of 2.5 centimeters and containing a charge 11 of an alkali metal halide of coarse particle size. Below the reaction vessel is the bottom vessel 12 for receiving the final product, which is removed continuously or periodically through a discharge pipe 14. The upper end of the reaction vessel is closed to the exterior by a by-pass 17, in which an inert atmosphere of nitrogen from a flask 16 is maintained. The nitrogen is dried with phosphorus pentoxide in a vessel 18. The pentachloride is contained in an evaporator 20 which is connected through a pipe 22 to the bottom flask 12. The evaporator 20 is immersed Within a salt bath 24 heated by a heating device 25. The bottom vessel 12, a connecting tube 13 and the reaction vessel are each provided with a heating jacket 26, 28 and 30, respectively.

In FIGURE 2 is shown diagrammatically an apparatus for making reduced double salts. This apparatus comprises a vertical reaction vessel 110 having a charge 112 of alkali metal chloride of coarse particle size. Below the reaction vessel is provided a bottom vessel 114 to receive the final product, which is continuously or periodically removed. Hydrogen is supplied through a pipe 115 to an evaporator 116, in which the metal pentachloride is vaporized by means of a thermostatic heater 118. The hydrogen is dried in vessels 120 and 122, and oxygen is catalytically removed from the hydrogen in a vessel 124. Connected to the upper end of the reaction vessel is a cooler for the unreacted metal pentachloride leaving the upper part of the vessel, and a valve 128 is provided to prevent air entering the cooler 126. The reaction vessel 110 and the bottom flask 114 are each provided with heating jackets 130 and 132 respectively.

Example 1 138 grams of niobium pentachloride were introduced into the evaporator shown in FIGURE 1. The reaction vessel 10 was charged with potassium chloride having a particle size of about 2-10 mm. The salt bath 24 was brought to a temperature of 270 C. The bottom vessel 12 was heated to 410 C., the vessel 10 to 465 C. and the connecting tube 13 to a temperature of about 500 C. The reaction was continued until the whole of the pentachloride contained in the evaporator 20 had been vaporized. In the bottom vessel 12 there were then 185 grams of the double salt. This double salt had a melting point not appreciably below 400 C. For the purpose of analysis the double salt was thermally decomposed at 700 C., the pentachloride thus liberated was withdrawn by means of nitrogen and its Weight was determined in the form of the oxide. The residue of potassium chloride left behind by the decomposition was weighed. These analyses gave the composition of the double salt as consisting of 79.3% of niobium pentachloride and 21.8% of potassium chloride. These percentages are very close to the theoretical percentages of 78.4% and 21.6%, respectively, for the double salt having the formula NbKCl The yield of the double salt was 95.2% calculated on the pentachloride used.

Example 2 218 grams of tantalum pentachloride were introduced into the evaporator 20 of the apparatus used in Example 1. The temperature of the evaporator was slowly raised to 300 C. until the whole of the pentachloride had been vaporized. The bottom vessel 12 was heated to 470 C., the reaction vessel 10 to 490 C. and the connecting tube 13 to 500 C. After the reaction, there were present in the bottom vessel 233 grams of the double salt which had a melting point of about 420 C. For the purpose of analysis the double salt was thermally decomposed at about 700 C. and the liberated pentachloride and the residual potassium chloride were weighed. The double salt was found. to contain 82.5% by Weight of tantalum pentachloride and 16.5% by weight of potassium chloride, these percentages agreeing very closely with the theoretical values of 82.8% and 17.2%, respectively, for a double salt having the formula TaKCl The yield of the double salt was 87.5% calculated on the pentachloride used.

Example 3 A reaction column having a length of 60 cm. and an internal diameter of 5 cm. was charged with 400 grams of dry potassium chloride having a particle size equal to or greater than 2 mm. 228 grams of tantalum pentachloride were introduced into the evaporator and were maintained at a temperature of 210 C. by a thermostatically controlled heater. Hydrogen was passed through the pentachloride at a rate of 0.5 liter per minute. The reaction column was maintained at 730 C. The reduced product leaving the column had a temperature of 685 C. In the course of 4 hours a total of 217 grams of tantalum pentachloride were vaporized, of which 211 grams were converted into double salt and 6 grams were precipitated after leaving the reaction column.

A total of 307 grams of product Were collected in the bottom vessel. This product had the following analysis:

Percent by weight K 21.8 Ta 33.0 C1 44.45

which corresponds to the empirical formula K TaCl The liquefaction point of this eutectic mixture was 610 C. Its X-ray diagram showed in addition to the potassium chloride lines the lines of a cubic flat-centered latice, of which the length of the edge was about 10 Angstrom units. This corresponded to the double salt of the formula K TaCl The product was therefore a eutectic mixture of potassium chloride and the reduced (tetravalent) double salt.

Example 4 The reaction column used in Example 3 was charged with 250 grams of dry potassium chloride having a particle size within the range of 2-5 mm. In the evaporator niobium pentachloride was heated at C. Hydrogen was passed through the pentachloride at the rate of 1.0 liter per minute. The reaction column was maintained at a temperature of 730-740" C. The product flowed from the column at a temperature of 680690 C.

In the course of 4 hours a total of 248 grams of niobium pentachloride was evaporated, of which 3 grams were precipitated after leaving the column. A total of 370 grams of product having a liquefaction point of about 652.5 C. was obtained. It had the following analysis:

Percent by weight K 27.90 Nb 21.55 Cl 50.25

This analysis corresponded to the empirical formula NbCl .3KCl. The niobium in the product was therefore trivalent. The product was obtained in a yield amounting to 75% calculated on the metal introduced as pentachloride.

What is claimed is:

l. In a process for producing lower valency tantalum potassium double chloride, from higher valency tantalum chloride and potassium chloride, the improvement of contacting a stream of hydrogen with tantalum pentachloride at a temperature in the vicinity of the melting point of the latter and passing the resulting stream of hydrogen laden with tantalum pentachloride vapor upwardly through a reaction zone of solid granular potassium chloride having a particle size of about 2 millimeters and larger, while heating said zone at a temperature above 610 C. and below the melting point of potassium chloride, and allowing the 5 formed liquid double salt to flow out of the reaction zone downwardly into a collecting zone below the reaction zone.

2. The improvement as claimed in claim 1, wherein the reaction zone is held at a temperature of about 730 C.

3. The improvement as claimed in claim 1, wherein the tantalum pentachloride contacted by hydrogen is heated at about 210 C., and the flow rate of the hydrogen stream is about 0.5 liter per minute.

4. In a process for producing lower valency niobium potassium double chloride from hi her valency niobium chloride and potassium chloride, the improvement of contacting a stream of hydrogen with niobium pentachloride at a temperature in the vicinity of the melting point of the latter and passing the resulting stream of hydrogen with niobium pentachloride vapor upwardly through a reaction zone of solid granular potassium chloride having a particle size of about 2 millimeters and larger, while heating said zone at a temperature above 652.5" C. and

References Cited in the file of this patent UNITED STATES PATENTS 2,469,916 Carter May 10, 1949 2,725,278 Polissar Nov. 29, 1955 2,891,857 Eaton June 23, 1959 2,974,007 Scheller Mar. 7, 1961 

1. IN A PROCESS FOR PRODUCING LOWER VALENCY TANTALUM POTASSIUM DOUBLE CHLORIDE, FROM HIGHER VALENCY TANTALUM CHLORIDE AND POTASSIUM CHLORIDE, THE IMPROVEMENT OF CONTACTING A STREAM OF HYDROGEN WITH TANTALUM PENTACHLORIDE AT A TEMPERATURE IN THE VINCINITY OF THE MELTING POINT OF THE LATTER AND PASSING THE RESULTING STREAM OF HYDROGEN LADEN WITH TANTALUM PENTACHLORIDE VAPOR UPWARDLY THORUGH A REACTION ZONE OF SOLID GRANULAR POTASSIUM CHLORIDE HAVING A PARTICLE SIZE OF ABOUT 2 MILLIMETERS AND LARGER, WHILE HEATING SAID ZONE AT A TEMPERATURE ABOVE 610* C. AND BELOW THE MELTING POINT OF POTASSIUM CHLORIDE, AND ALLOWING THE 